Method of making tools and the like from sintered hard-metal carbides or like materials



Patented Apr. 2, 1935 UNITED STATES METHOD OF MAKING TOOLS AND THE LIKE FROM SINTERED HARD-METAL CARBIDES OR LIKE MATERIALS Kjell Magnus Tigerschiiild and Giista Sterky,

.- Fagersta, Sweden N6 Drawing. Application November 3, 1932,

Serial No. 841,117 1931 a 8 Claim.

This invention relates to improvements in the manufacture of tools and other objects subjected to abrasion, from sintered hard metal carbides or like material.

It has been known to make form pieces for tools from sintered carbides of hard metals or like materials. After final sintering such form pieces are extraordinarily hard and diflicult to work, and, if they are to be made in a complicated shape, the making of same becomes very diflicult and expensive. On making the said form pieces one generally proceeds from a mixture of very hard powders, consisting of carbides, nitrides, borides or silicides of such hard metals as Cr, W, Mo, Ti, Ta, V, Nb, Zr and U, mixed with softer metal powders, most oftenly of a lower melting point, such as powders of Ni, Co or Fe. The purpose of the additional metals is partly to facilitate the sintering of the pulverous hard material to a dense body of a considerable hardness, partly to increase the toughness of the material. Moreover other metals as for instance W, Mo, Ti or V may be added.

In making tools of this kind, it has previously proved to be advantageous first to press the powder in question to a form piece, which in different ways is caused to cohere so well that a preliminary treatment by means of material-removing tools can be effected. After such a treatment the final sintering takes place, after which further working of the form piece may be done only with difficulty. Many different ways have hitherto been proposed to obtain formv pieces in a workable form.

According to one method a solidifying binder, such as dextrine or shellac, has been added to the pulverous material, and from the simple form piece obtained by a pressing operation the tool has been given the shape desired by means of mechanical treatment after solidification of the binder. However, this method has proved not to be suitable in practice, partly as it is very hard to obtain a homogeneous distribution of the binder in the form piece, partly as the product is easily made impure by the percentage of ash of the binder.

According to another known procedure, which also comprises a purely physical actuation upon the simple form pieces, the said form pieces are subjected to a heating up to a temperature of 700-ll C., at which temperature the added auxiliary metal (Fe, Co, or Ni) acquires a binding effect. After such a preliminary treatment the form pieces may be worked by ordinary tools,

In Sweden November 4,

but during the working the said tools are subjected to a very hard wear and tear.

As another method it is also known, by means of pressing at very high pressures-hydraulic pressing from all sides-to obtain form pieces, having a suflicient strength to be worked. However, this method requires very expensive apparatus and is complicated.

Finally by carrying out the pressing at a somewhat raised temperature a slight coherence of the product may be obtained. However, also this method is complicated and expensive, and difficulties easily arise to obtain a uniform product.

The present invention relates to a process of making tools and the like from a pulverous mixture, which consists of a hard metal carbide, boride, silicide, or nitride, and one or more softer added auxiliary metals, ,such as iron, cobalt, or nickel, possibly together with one or more hard metals, such as tungsten, molybdenum, titanium, or vanadium, the final shape by mechanical working being given after the said mixture has been pressed to a form piece, after which working the final sintering is efiected.

According to the invention, the mixture is subjected, before, after, or during the pressing, to the influence of such substances as with a chlorinating action attack the surfaces of the powder of the auxiliary metal, for example by addition of or treatment by chlorides, so that a coherent form piece is obtained, which is worked and then, possibly after the portion of the chlorinating substances which is still present has been expelled and the compounds formed have been decomposed for instance by reduction, and possibly after a subsequent pressing, is subjected to the final sintering.

By such chemical action upon the metal surfaces a coherence is obtained, completely satisfying all requirements for a good workability and for a sumcient strength. Such chemical action can be effected both at ordinary and also at raised temperatures.

The converting of the metal surfaces into chlorides may for instance be effected by mixing the pulverous mixture with dry powdered ammonium chloride; the powdered ammonium chloride may also be mixed during the grinding together of the hard particles with the softer auxiliary metal. of course, the pulverous mixture may also be moistened by means of a solution of ammonium chloride either in water or in suitable organic solvents, such as methyl alcohol or the like.

After such a treatment, the form pieces become sufficiently well bound together to enable them to be worked to the desired shape. In many cases, however, it has proved to be suitableto employ heat treatment after the pressing but before the mechanical working to desired shapes, possibly in combination with the expelling of parts of the chlorinating substances which are still present or decomposition of the compounds formed, for instance by reduction. In most cases, the said treatment may be carried out with the effect desired at a very low temperature, in any case below 600 0., preferably at 400-500 C. The product obtained may in this way be given an extraordinary suitable consistency for the working intended, and the wear and tear of the tool used becomes extremely small.

The method may be varied in dlfierent ways: The procedures mentioned must be regarded only as examples. It should be noticed that it is suitable to remove from the product the reaction products obtained in the form of gas and without it being necessary to raise the temperature too high, since a removal of heavy salts at high temperatures will easily cause the formation of blow holes in the material.

By tests the inventors have shown that for instance a solution of ammonium chloride cannot be looked upon as a solidifying binder. A powder consisting only of a tungsten carbide cannot be bound together by adding a solution of ammonium chloride. Moreover, the inventors have found that the strength of the product increases after heating the form pieces in an atmosphere of hydrogen at a. temperature above the point of sublimation of the ammonium chloride. Probably some cobalt chloride is formed, which is not expelled or decomposed at a temperature below 600 C. The reaction causing the form' piece to cohere takes place even on adding exceedingly small quantities of the reagent.

In certain cases it has proved to be suitable after the heat treatment below 600 C. to subject the material to a new pressing together, by which its consistency becomes firmer and especially suitable for working to complicated tools. In such a case the first pressing is carried out at a relatively low pressure, for example 1000 kgs/cm, the second pressing operation after the heat treatment taking place at a considerably higher pressure, for example 10,000 kgs/cm.

As might be seen from the above description the method is very simple and inexpensive to carry out. I

In the annexed claims, it is understood that the step of chlorinating may take place prior to, during. or subsequent to, the step of pressing.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

1. The process of making solid bodies from a pulverous mixture, which comprises mixing a comminuted compound of a hard metal, such as tungsten, tantalum, or titanium, and a metalloid, such as carbon, boron, or nitrogen, and at least one softer additional metal, such as iron, cobalt, or nickel, chlorinating the softer additional metal with ammonium chloride, and pressing the mixture into form pieces which are worked to the desired shape.

2. The process set forth in claim 1, wherein the pulverous mixture contains, in addition, a hard metal, such as tungsten, tantalum, or titanium in metallic form. I

3. The process set forth in claim 1, wherein the chlorination takes place at a temperature not exceeding 600 C.

4. The process set forth in claim 1, comprising, in addition, the step of dechlorinating the body.

5. The process set forth in claim 1, comprising, in addition, the step of expelling the excess of chlorinating substances by heating at a temperature below 600 C.

6. The process set forth in claim 1, wherein the pulverous mixture contains, in addition, ammonium chloride.

7. The process set forth in claim 1, wherein the pulverous mixture contains, in addition, dry powdered ammonium chloride.

8. The process set forth in claim 1, wherein the pulverous mixture contains, in addition, a solution comprising ammonium chloride.

KJELL MAGNUS ncmnscrnom. G6STA STERKY. 

